Around the time of puberty the body undergoes a lot of changes, some functions have to be relearned. Both boys and girls have problems, very nearly everyone starts and ends in nappies/diapers, so do not worry about teen incontinence , in most cases time sorts it out.
For other cases, many people have an horrendous diet, toilets are too high, I am 1.9m tall and still find some toilets are too high for me to be able to go! so consider the problems a child has with an adult size toilet!!
Bullying at school, many factors combine to make school toilets a no go area, so do not take it out on the child, change schools, go private, home school, anything but make it worse for a already troubled and frightened child.
Adults in nappies, well over a certain age things start to go wrong, fall apart.
AB/DL hum, people may start as these. But end up being true 24/7 which is not a lot of fun! Try looking after an elderly person who is 24/7 and weighs more than yourself, on your own, means also that yourself has no control on when you can go or when you go, that time has passed-on, so better! Still in nappies at night, but at least no longer during the day.
Other solutions, try walking at least three miles a day, worked for me. Also consider dog walking, reasons, works with humans also, drink plenty, go for a walk, if you make it back before you go good!
Many problems with humans are due to not enough exercise, poor diet and not drinking enough!